The invention is directed to a fuel delivery system for aerospace vehicles and more particularly to fuel delivery on horizontal takeoff and hypersonic hydrogen fueled aerospace vehicles which contain slush hydrogen fuel and/or encounter significant aerodynamic heating during takeoff and flight.
FIG. 1, identified as prior art, shows a typical liquid feed fuel system. All fuel used by the engines is removed from the tank as liquid and delivered to the main turbo-machinery through a boost pump. The liquid is pumped to high pressure in the turbo-pump and used for active cooling of the engine and/or airframe as required. This heated fuel is then expanded through a turbine, to obtain shaft work required for the pump, before being burned in the combustor.
Tank pressure is normally maintained by pressurizing the ullage with recirculated hot hydrogen. Alternatively, venting of the fuel tank to the atmosphere will be required if environmental heating of the fuel produces more vapor then is required to displace liquid fuel outflow. This vaporized fuel is wasted by the venting. Maintaining the tank in a stratified state with a hot ullage is desirable to minimize heating of the liquid fuel, minimize trapped vapor residuals and increase the amount of energy extracted from the tank per unit of mass vented. However, tank pressure control is complicated by the stratified ullage. Disturbances caused by vehicle maneuvering, flight through turbulent atmosphere and changes in the lift/thrust ratio will cause cold liquid fuel to be splashed onto the hot tank walls and mixed with the hot ullage gas. Quenching of the tank wall in this manner will cause rapid vaporization of the liquid accompanied by rapid pressure rise. Mixing of liquid with the ullage will cool the ullage gas and cause fuel tank pressure to fall. These effects have been predicted and observed on cryogenic launch vehicles such as, for example, the Centaur vehicle. Mix/quench pressure excursions are tolerated on vehicles, such as the Centaur vehicle, by minimizing liquid fuel disturbances and assuring adequate structural margins to accommodate the pressure fluctuations that may occur.
There has not been a successful means or method for complete and efficient utilization of onboard fuel for aerospace vehicles, which experience significant fuel tank heating until the emergence of the instant invention.